DSOL ITPA meeting W.Fundamenski Avila, Spain, 7-10/01/08

H-phase in ITER: what can be learned about divertor and SOL behaviour in the D and D-T phases

W. Fundamenski (UKAEA, EFDA-JET)

DSOL ITPA meeting W.Fundamenski Avila, Spain, 7-10/01/08

Coupled system of ions, electrons, neutrals and fieldsCoupled system of ions, electrons, neutrals and fields

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Kinetic equation for electrons, ions, impurities and neutrals

Accelaration due to both internal and external fields

Coulomb collisions for charged species, described by the Fokker-Planck operator, neutral collisions by the Boltzmann operator

Maxwell’s equations for internal fields

Closure only via 0th and 1st

Suggests the moment approach

Complex system of i, e, n and Complex system of i, e, n and

DSOL ITPA meeting W.Fundamenski Avila, Spain, 7-10/01/08

– fully ionised plasma physics (dimensionless parameters), scaling with ion mass • All electron quantities independent of A, e.g. e e vTe e A0 const

• Ion quanties typically scale as a square root (or its inverse) of the ion mass, e.g. * 1/* 1/vTi 1/vA 1/||i e A1/2, i A0 const• The combination of these include the range of derived quantities, including plasma-neutral interactions (cross-sections) • D and H are chemically identical (to fairly high accuracy), hence electron impact reactions are quite similar (ionisation, excitation, etc).• In contrast, ion impact reactions can differ substantially, eg. CX, elastic scattering.

– plasma-surface interactions (erosion yields)• Physical sputtering of C, Be, W,… depends on ion mass• Chemical sputtering of C comparable for H and D

– SOL plasma transport• Parallel convection at roughly the plasma sound speed, cs vTi A-1/2

• Parallel conduction, ||i A-1/2

Ion mass in edge/SOL plasma physicsIon mass in edge/SOL plasma physics

DSOL ITPA meeting W.Fundamenski Avila, Spain, 7-10/01/08

plasma

neutrals

fields (photons)

surface

Tokamak core is largely a classical, fully ionised plasma (relativistic corrections for runaway electrons, quantum corrections for impurities)

Tokamak edge involves quantum effects due to interaction of ions-electrons, photons, atoms-molecules and solid surface (eg. ionisation-recombination, excitation-emission, charge exchange, surface chemistry,…)

The relative importance of quantum effects complicates a general theory of a tokamak edge plasma, which is typically described by severely truncated forms

Interactions in the tokamak edgeInteractions in the tokamak edge

DSOL ITPA meeting W.Fundamenski Avila, Spain, 7-10/01/08

1) e + H2 H2+ + 2e

2) e + H2 2H0 + e

3) e + H2 H0 + H+ + 2e

4) e + H2+ 2H0

5) e + H2+ H0 + H+ + 2e

6) e + H0 H+ + 2e

7) H0 + H+ H+ + H0

In practice, quantum effects included via interaction cross-sections

Selected plasma-neutral cross-sectionsSelected plasma-neutral cross-sections

DSOL ITPA meeting W.Fundamenski Avila, Spain, 7-10/01/08

– Due to the complexity of the above scalings, a simple ‘wind-tunnel’ similarity experiment not possible within a single machine• i.e. not possible to directly extrapolate from the H-phase to the D-phase of ITER based on a simple dimensionless scaling

– However, all of the above scalings can be (are) included in edge transport codes, • multi-fluid plasma/MC neutrals codes, eg. SOLPS (B2/EIRENE), …• local or global turbulence codes, e.g. ESEL, GEM, XG2, etc. • plasma filament transport,

– Therefore, from the DSOL perspective, the validation of these codes should be the primary task of the H-phase in ITER, • For instance, consider divertor plasma detachment (discussed on Monday)

– Once validated, the extrapolation to ITER D phase becomes more credible from the ITER H-phase, then from, say, the JET D phase, e.g. *, div.closure, etc.– To facilitate this extrapolation in the ion mass, it is desirable to perform reference (matched) H vs D experiments in existing tokamaks,

• The focus should be on Ohmic and L-mode edge/SOL conditions, in order to empirically infer (whenever possible) isotopic scalings of unknown plasma parameters• This should be supplemented by detailed modelling effort

Extrapolation to ITER D-phaseExtrapolation to ITER D-phase